Irresistible irises: Secrets to eight weeks of blooms

It’s an intoxicating experience to visit a bearded iris garden in flower. The genus Iris is named for the Greek goddess of the rainbow, which is apt because no other perennial rivals them for their range of colours—and the bearded types (named for their fuzzy fall) are the most opulent of them all. Set off by handsome sword-like leaves, their ruffled blooms cover the spectrum from blues, yellows and vibrant pinks to glowing white and almost black. There are shades of gold, apricot, orange, russet and dusky burgundy, but not pure red. Colours appear even richer when outlined with margins of yellow or white, or dramatic streaks of contrasting colour. Some cultivars are even sweetly scented.

Plant expert Allan Armitage writes: “If an award were presented to most popular perennial with too many choices, the bearded iris would be the winner.” Modern varieties originate from crosses made using many species—including I. germanica, I. pallida and I. florentina—bred over many decades. These are not your grandmother’s irises: they have stronger stems and more blooms that last over a longer period.

In fact, while individual plants will flower for a week or two, with careful planning and a selection of early-, mid- and late-blooming varieties, you can stretch the bearded bloom season to about eight weeks, say growers Ann and Bob Granatier of Trails End Iris Gardens near Brantford, Ontario. “Here in our gardens, blooming begins in late April with dwarf cultivars and ends in late June with the stately tall beardeds,” says Ann. “As a bonus, there are varieties that rebloom in late summer.”

Most bearded irises are hardy to Zone 3. They need six hours of full sun daily and light, well-drained soil. If you have clay soil, lighten its texture by adding plenty of coarse sand and compost or composted manure.

Planting TipsIrises grow from rhizomes (thick underground stems) that sit horizontally at or just below ground level. The true roots come out of the rhizome and penetrate the soil. You can plant potted irises in spring and bare-root ones in midsummer as they become available. Buying bare-root rhizomes is more cost-effective; however, the Granatiers recommend getting them into the ground by mid-August.

Most planting instructions advise you to not cover the rhizome with soil, as it likes to bask in the sun. But Chuck Chapman, vice-president of the Canadian Iris Society and an iris grower and hybridizer with 20 years of experience, disagrees. In regions without reliable snow cover but frequent winter freeze/thaw cycles, he recommends covering them with about 2.5 centi-metres of sand.

“I’ve tested this method over three years and we get less frost heave and rot,” explains Chapman. “Soil on top of the rhizomes keeps the temperature more uniform, so tears in the plants’ tissues are less likely.” The Granatiers cover new iris rhizomes with 2.5 to five centimetres of sand. Avoid mulching with wood chips or leaves; soil or sand will drain, but most mulches stay too wet.

Spacing: Set rhizomes 40 to 45 centimetres apart for taller types, 20 to 25 centimetres for dwarf varieties; arrange in triangular groups of three or five so the growing point on the rhizome faces outward. For good air circulation, position groups 60 to 72 centimetres away from other plants.

Pot-grown irises: Gently remove from pot; do not disturb roots. Plant at same level as iris was in the container.Bare-root irises: Dig a hole as deep as rhizome’s true roots. Make a small mound of soil inside planting hole, high enough to position rhizome on mound at ground level or slightly below; cover roots with soil.After planting, water well and continue to irrigate every three days for a week or two depending on rainfall—irises need about two centimetres of water twice a week.